This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Patent Application No. 2000-197968, filed on Jun. 30, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a hydraulic brake apparatus for a vehicle which feeds hydraulic brake pressure in wheel cylinders provided on each wheel of the vehicle. More particularly, the present invention pertains to a vehicle hydraulic brake apparatus for a vehicle that includes a master cylinder section, an auxiliary hydraulic pressure source and a pressure regulating device.
A known hydraulic brake apparatus for an automobile is disclosed in U.S. Pat. No, 5,899,068, which corresponds to a Japanese Patent Application published as Toku-Kai-Hei 9 (1997)-315288. This known hydraulic brake apparatus includes a master cylinder, an auxiliary pressure source, and a pressure regulating valve section. The master cylinder piston is provided with a first piston connected to a brake operating member (brake pedal) and a second piston slidably disposed relative to the first piston. The master cylinder piston further includes an engaging portion for engaging the second piston with the first piston in response to forward movement of the second piston. The rear ends of the first piston and second piston are exposed to a power chamber, and the front ends of the first piston and the second piston are exposed to a pressure chamber. The master cylinder is assisted and activated by an output hydraulic pressure from the pressure regulating valve section in response to the operation of the brake operating member when an output hydraulic pressure supplied from the auxiliary pressure source is sufficient. On the other hand, the master cylinder is activated directly in response to operation of the brake operating member when the output hydraulic pressure supplied from the auxiliary pressure source is insufficient. Therefore, the known hydraulic brake apparatus can carry out an appropriate braking control only by the master cylinder even when sufficient power hydraulic pressure is not supplied. When the output hydraulic pressure is not sufficiently supplied from the auxiliary pressure source, only the first piston is moved forward. On the other hand, when sufficient output hydraulic pressure is supplied from the auxiliary pressure source, both the first and second pistons are moved forward. Therefore, when the output hydraulic pressure from the auxiliary pressure source is insufficient, an effective cross-sectional area of the master cylinder piston can be minimized compared with that when the output hydraulic pressure from the auxiliary pressure source is sufficient. Therefore, the hydraulic pressure in the pressure chamber can be sufficiently increased even when the output hydraulic pressure supplied from the auxiliary pressure source is not sufficient.
Additionally, the second piston is in the form of a cylindrical body, the front end of which is disposed in the pressure chamber and the rear end of which is disposed in the power chamber. The first piston is slidably received in a hollow portion of the cylindrical body forming the second piston. Therefore, the master cylinder piston, including the first and second pistons, is formed as a double-piston structure. A closed chamber is defined between the first and second pistons, and communicating holes connect the closed chamber to the pressure chamber or the power chamber. According to the communication between the closed chamber and the pressure chamber or the power chamber, a shock generated by separation or engagement of the first and second pistons in response to a sudden operation of the brake operating member can be minimized.
The pressure regulating valve included in the known hydraulic brake apparatus is constructed as a so-called regulator. Alternatively, a hydraulic pressure booster can be used as the pressure regulating valve. For example, according to U.S. Pat. No. 5,029,951 (corresponding to a Japanese Patent Application published as Toku-Kai-Hei 2 (1990)-95966), the hydraulic brake apparatus is provided with a hydraulic pressure booster for assisting the master cylinder to be activated in response to the brake pedal depression by using the output hydraulic pressure supplied from a power hydraulic pressure source (the auxiliary pressure source) as an assisting power source. The above-mentioned hydraulic brake apparatus includes a power piston and the master cylinder which have diameters different from each other and the closed chamber hydraulically connecting the power piston to the master cylinder. According to the above construction, the brake pedal stroke can be minimized. Further, the master cylinder can be activated directly by the brake pedal when the hydraulic pressure booster is unable to generate sufficient assisting pressure force.
The hydraulic pressure booster according to the Japanese Patent Application published as Toku-Kai-Hei 2 (1990)-95966 includes a one-way valve disposed between the power chamber of the hydraulic pressure booster and the closed chamber. When the hydraulic pressure booster cannot generate sufficient assisting pressure force, the power piston can be operatively connected to the master piston. Further, a check valve and a cup-like sealing member function as the one-way valve according to the above known hydraulic brake apparatus.
Further, the one-way valve is provided for allowing communication between the closed chamber and the power chamber in response to the pressure differential between the two chambers. However, the publication describing the known device does not disclose the details of the non-operated condition of the hydraulic brake apparatus. For example, under the non-operated condition, communication between the closed chamber and the power chamber is interrupted by the one-way valve formed by the cup-like sealing member or by a normally used check valve.
It is favorable if the communication between the closed chamber and the power chamber is established and the closed chamber is connected to a reservoir via the power chamber when the hydraulic brake apparatus is in the non-operated condition. Therefore, when the closed chamber is required to be filled with brake fluid, an evacuation of the air in the closed chamber can be carried out easily and accurately by air bleeding from an opening in a reservoir, maintaining the inside of the hydraulic brake apparatus at a high vacuum condition and transmitting pressured brake fluid to the closed chamber. However, the hydraulic pressure booster is provided with the check valve having a pressure for valve opening between the closed chamber and the power chamber. Therefore, brake pedal operation is required to carry out the air bleeding.
According to the hydraulic brake apparatus described in U.S. Pat. No. 5,899,068, the master cylinder including the first and second pistons is formed as a double-piston structure. The closed chamber is defined between the first and second pistons of the master cylinder piston. The closed chamber serves to minimize shock generated by separating or engaging the first and second pistons in response to a sudden operation of the brake operating member. Therefore, the closed chamber according to U.S. Pat. No. 5,899,068 serves a different function from that disclosed in U.S. Pat. No. 5,029,951. Further, the closed chamber according to U.S. Pat. No. 5,899,068 does not encounter as much difficulty in carrying out the air bleeding for filling the closed chamber with brake fluid.
According to one aspect of the invention, a hydraulic brake apparatus for a vehicle includes a brake operating member, a reservoir, a master cylinder for generating a brake hydraulic pressure by increasing the pressure of the brake fluid in the reservoir, a master piston moved forward in response to the brake operating member operation, a closed chamber defined behind the master piston, a power piston disposed behind the master piston and a power chamber defined behind the power piston. The hydraulic brake apparatus further includes an auxiliary hydraulic pressure source for generating a power hydraulic pressure by increasing the brake fluid up to a predetermined hydraulic pressure, and a pressure regulating device for connecting the auxiliary hydraulic pressure source with the reservoir. The output power hydraulic pressure of the auxiliary hydraulic pressure source is regulated to be set at the predetermined hydraulic pressure and is fed into the power chamber. A normally open-type valve connects the closed chamber and the power chamber, and is adapted to be closed in response to initiation of the brake operation. The closed chamber is connected to the reservoir via the normally-open type valve, the power chamber and the pressure regulating device.
According to another aspect of te invention, a hydraulic brake apparatus for a vehicle includes a brake operating member, a reservoir, a master piston movably positioned within a cylinder bore to move in response to operation of the brake operating member, a closed chamber located rearward of the master piston, a power piston disposed rearward of the master piston, a power chamber defined by the power piston and two sealing members, a passage connecting the power chamber and the closed chamber, and a pump connected to the reservoir to generate power hydraulic pressure by increasing the pressure of the brake fluid from the reservoir to a predetermined hydraulic pressure. A pressure regulating device is connected to the auxiliary hydraulic pressure source and to the reservoir to regulate the power hydraulic pressure from the auxiliary hydraulic pressure source to a predetermined hydraulic pressure and feed the regulated the power hydraulic pressure to the power chamber. A valve is located in the passage to close off the passage and interrupt communication between the power chamber and the closed chamber by way of the passage based on either movement of the power piston or a pressure differential between the power chamber and the closed chamber. The closed chamber is connected to the reservoir via the valve, the power chamber and the pressure regulating device.
In accordance with a further aspect of the invention, a hydraulic brake apparatus for a vehicle includes a brake operating member, a reservoir, a master piston movably positioned within a housing and movable in response to operation of the brake operating member, a closed chamber located rearward of the master piston, a power piston disposed rearward of the master piston, a power chamber defined by the power piston and in communication with the closed chamber by way of a communicating space, and a pump connected to the reservoir to generate power hydraulic pressure. A pressure regulating device is connected to the auxiliary hydraulic pressure source and to the reservoir to regulate the power hydraulic pressure from the auxiliary hydraulic pressure source to a predetermined hydraulic pressure and feed the regulated the power hydraulic pressure to the power chamber. A normally open valve is positioned to close the communicating space and interrupt communication between the power chamber and the closed chamber upon operation of the brake operating member.